More than 40 years ago, in 1977, someone walked into the Delaware State Museum in Dover during visiting hours, broke into a display case containing moon dust from the Apollo 11 mission and got away with one of the museum's most priceless artifacts.

"It was reported to the police at the time, and it has not been seen since," said Jim Yurasek, spokesman for the Delaware Division of Historical and Cultural Affairs. "Unfortunately, we haven't heard a thing."

With the 50th anniversary of the Apollo 11 space mission just around the corner, attorney, moon rock hunter and Houston-based professor Joseph Gutheinz is on the hunt for Delaware's missing moon dust.

The strange thing is, it wasn't the only theft. President Richard Nixon's administration presented the tiny lunar samples to all 50 states and 135 countries, but few were officially recorded and most either disappeared or were stolen, Gutheinz said.

Now, after years of sleuthing, the former NASA investigator is closing in on his goal of locating the whereabouts of all 50.

"It's a tangible piece of history," he said. "Neil Armstrong's first mission ... was to reach down and grab some rocks and dust in case they needed to make an emergency takeoff."

Nixon had personally given the moon dust to Delaware in 1969. It, and a small Delaware state flag that was carried to the moon on Apollo 11, were encased in plastic, attached to a plaque and put on display in the Delaware State Museum.

The moon dust was stolen on Sept. 22, 1977. A museum worker discovered the theft and police found two of the four nails used to affix the plastic cover to the plaque on the floor, according to media reports.

Though the crime took place four decades ago, Gutheinz is determined to solve it. And there may be hope.

In recent weeks, two moon rocks that disappeared after the 1969 mission were located in Louisiana and Utah, leaving only New York and Delaware with unaccounted-for souvenirs.

When Gutheinz started leading the effort to find the artifacts in 2002, he estimates 40 states had lost track of their rocks.

"I think part of it was, we honestly believed that going back to the moon was going to be a regular occurrence," Gutheinz said.

This photo shows moon rocks encased in acrylic and mounted on a wooden plaque at the Clark Planetarium, in Salt Lake City.(Photo: Rick Bowmer, AP)

But there were only five more journeys before the last manned moon landing, Apollo 17, in 1972. Of the Apollo 11 rocks given to other countries, about 70 percent remain unaccounted for, he said.

The U.S. government sent out a second set of goodwill moon rocks to the states and other nations after the Apollo 17 mission, and while many of those are missing, as well, Delaware's is not, Yurasek confirmed Thursday.

“We do have a rock from a subsequent Apollo mission," he said. "We don’t put it on display anymore.”

Lindsie Smith, from the Clark Planetarium, holds moon rocks encased in acrylic and mounted on a wooden plaque at the Clark Planetarium, in Salt Lake City. A former NASA investigator who has spent more than a decade tracking missing moon rocks is closing in on his goal of finding all 50 lunar samples gifted to U.S. states after Neil Armstrong's first steps on the moon. In recent weeks, two more of the moon rocks that dropped off the radar after the 1969 Apollo 11 mission have been located in Louisiana and Utah.(Photo: Rick Bowmer/AP)

Gutheinz began his career as an investigator for NASA, where he found illicit sellers asking millions for rocks on the black market. Authentic moon rocks are considered national treasures and cannot legally be sold in the U.S., he said.

He became aware while at NASA that the gifts to the states were missing, but only began his hunt after leaving the agency.

Now a lawyer in the Houston area, he's also a college instructor who's enlisted the help of his students. They record their findings in a database.

Many of the Apollo 11 rocks have turned up in unexpected places: with ex-governors in West Virginia and Colorado, in a military-artifact storage building in Minnesota and with a former crab boat captain from TV's "Deadliest Catch" in Alaska.

This 2018 photo shows a plate mounted on a wooden plaque that holds moon rocks encased in acrylic at the Clark Planetarium, in Salt Lake City.(Photo: Rick Bowmer, AP)

In New York, officials who oversee the state museum have no record of that state's Apollo 11 rock. The U.S. Virgin Islands territory cannot confirm that they ever received a goodwill rock, though the University of the Virgin Islands later received Apollo 11 rocks for scientific research, said chief conservator Julio Encarnacion III.

In other states, Gutheinz has recently hit paydirt. The Advocate newspaper in Baton Rouge located Louisiana's Apollo 11 moon rock in early August after a call from Gutheinz.

In Utah, the division of state history had no record of the sample but The Associated Press confirmed it was in storage at Salt Lake City's Clark Planetarium.

Officials there may bring it out as part of celebrations recognizing the Apollo 11 anniversary next year, something Gutheinz hopes to see everywhere.

"The people of the world deserve this," he said. "They deserve to see something that our astronauts accomplished and be a part it."

This story contains information originally reported by Associated Press writer Lindsay Whitehurst. Contact Jessica Bies at (302) 324-2881 or jbies@delawareonline.com. Follow her on Twitter @jessicajbies.